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941.
Hongyu Yang Xin Wang Lei Song Bin Yu Yao Yuan Yuan Hu Richard K. K. Yuen 《先进技术聚合物》2014,25(9):1034-1043
The main aim of this work was to investigate the synergistic effect of expandable graphite (EG) and aluminum hypophosphite (AHP) on the flame retardancy of rigid polyurethane foams (RPUFs). A series of flame retardant RPUF containing EG and AHP were prepared by one‐shot and free‐rise method. The flame retardant, thermal degradation, and combustion properties of RPUF hybrids were characterized through limiting oxygen index (LOI) test, vertical burning (UL‐94) test, thermogravimetric analysis and microscale combustion calorimeter. The LOI and UL‐94 results showed that the RPUF sample with 10 wt% EG and 5 wt% AHP passed UL‐94 V‐0 rating and reached a relatively high LOI value of 28.5%, which is superior over other EG/AHP ratios in RPUF at the equivalent filler loading. Microscale combustion calorimeter results revealed that the incorporation of EG and AHP into RPUF reduced the peak heat release rate and total heat release, thus decrease the fire risk of RPUF significantly. Incorporation of EG and AHP improved the thermal stability of RPUF as observed from the thermogravimetric analysis results and also enhanced the thermal resistance of char layer at high temperature from scanning electron microscopy and Raman spectroscopy. Moreover, it could be seen from thermogravimetric analysis/infrared spectrometry spectra that the addition of EG and AHP significantly decreased the combustible gaseous products such as hydrocarbons and ethers. Finally, the synergistic mechanism in flame retardancy was discussed and speculated. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
942.
Miao Zhao Yakai Feng Guang Li Yuan Li Yalong Wang Ying Han Xujun Sun Xiaohua Tan 《先进技术聚合物》2014,25(9):927-933
Addition‐cure silicone resin is considered as a good choice for light emitting diodes (LEDs); however, it has very poor adhesion to the substrate, which limits its practical application. A novel polysiloxane with self‐adhesion ability and higher refractive index for the encapsulating of high‐power LEDs is prepared and characterized. This polysiloxane containing vinyl groups, phenyl groups, and epoxy groups was synthesized by a sol‐gel condensation process from methacryloxy propyl trimethoxyl silane, γ‐(2,3‐epoxypropoxy)propytrimethoxysilane, and diphenylsilanediol under the catalysis of an anion exchange resin. Then, the resin‐type encapsulation material was prepared by hydrosilylation of methylphenyl hydrogen‐containing silicone resin and the newly synthesized polysiloxane material. The novel polysiloxane was characterized by 1H‐NMR and Fourier transform infrared spectroscopy. On the basis of higher refractive index, higher transparency, excellent thermal stability, and appropriate hardness, as well as good adhesive strength between the encapsulating material and the LED lead frame (polyphthalamide), the curable silicone resin‐type encapsulation material can be used as an encapsulant for LEDs. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
943.
He Xu Ye Wu Shi-xiao Jin Ye Wang Jin Han Xiao-lin Meng Hai-long Yuan 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2463-2470
The antibacterial activities of a kind of novel peptide from Plutella xylostella (pxCECA1) on methicillin-resistant staphylococcus aureus (MRSA) and Escherichia coli (E. coli) growth were investigated by microcalorimetry. The heat flow power–time curves of MRSA and E. coli growth in the presence of pxCECA1 were recorded using the 3114/3115 Thermal Activity Monitor Air Isothermal Calorimeter based on ampoule mode at 37 °C. Some parameters including growth rate constant k, maximum power output P max, total heat output Qt, generation time t g, growth inhibitory ratio I, and half-inhibitory concentration of the drugs IC50 were obtained to elucidate the antibacterial activity of pxCECA1. The results showed that k, P max, and Q t decreased, but I and t g increased or delayed with the increase in pxCECA1 concentration. The IC50 of pxCECA1 on E. coli was 6.122 μg mL?1 and MRSA was 7.809 μg mL?1. It could be concluded that pxCECA1 had stronger inhibitory effect on E. coli than MRSA. In vivo test was simultaneously performed using an E. coli and MRSA infection model to validate the antibacterial activity of pxCECA1. The results revealed that pxCECA1 with broad spectrum antimicrobial activities hopefully represented a class of promising substitute of antimicrobial agents. 相似文献
944.
Weizhao Hu Bibo Wang Xin Wang Hua Ge Lei Song Jian Wang Yuan Hu 《Journal of Thermal Analysis and Calorimetry》2014,117(1):27-38
Ethyl cellulose, a widely used bio-degradable shell material, microencapsulated ammonium polyphosphate (MAPP) was added to the bio-degradable poly(butylene succinate) (PBS) to improve its flame retardancy, compatibility, and thermal stability. The MAPP was well characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), water contact angle, and thermogravimetric (TG) analysis. The SEM results indicate the improved dispersion of MAPP into PBS matrix and the formation of the strong interfacial adhesion between MAPP and PBS than APP. With the incorporation of MAPP and char-forming agent into PBS, the limiting oxygen index of the composite was increased to 35.5 %, and the sample can pass the UL-94 V-0 rating, while the un-microencapsulated counterpart cannot reach the rating. The cone calorimeter test showed that the peak heat release rate was decreased by 46.7 % and the burning time was also prolonged compared to the pure PBS. The increased melt flow index and rheology test indicated the increase of viscosity and the improvement of anti-dripping properties. Moreover, the mechanical properties and thermal stability of MAPP composite were also obviously enhanced after the microencapsulation by mechanical, dynamical mechanical thermal analysis, and TG analysis. 相似文献
945.
Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms 下载免费PDF全文
Dr. Chin‐Yuan Chang Syue‐Yi Lyu Dr. Yu‐Chen Liu Ning‐Shian Hsu Dr. Chih‐Chung Wu Dr. Cheng‐Fong Tang Kuan‐Hung Lin Dr. Jin‐Yuan Ho Dr. Chang‐Jer Wu Dr. Ming‐Daw Tsai Dr. Tsung‐Lin Li 《Angewandte Chemie (International ed. in English)》2014,53(7):1943-1948
Streptothricin‐F (STT‐F), one of the early‐discovered antibiotics, consists of three components, a β‐lysine homopolymer, an aminosugar D ‐gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long‐lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high‐resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an FeII‐dependent double hydroxylation reaction converting L ‐Arg into (3R,4R)‐(OH)2‐L ‐Arg via (3S)‐OH‐L ‐Arg, while OrfR catalyzes an unusual PLP‐dependent elimination/addition reaction cyclizing (3R,4R)‐(OH)2‐L ‐Arg to the six‐membered (4R)‐OH‐capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT‐F by a feeding experiment. 相似文献
946.
Xian‐Kai Wan Shang‐Fu Yuan Zhi‐Wei Lin Prof. Dr. Quan‐Ming Wang 《Angewandte Chemie (International ed. in English)》2014,53(11):2923-2926
The chirality of a gold nanocluster can be generated from either an intrinsically chiral inorganic core or an achiral inorganic core in a chiral environment. The first structural determination of a gold nanocluster containing an intrinsic chiral inorganic core is reported. The chiral gold nanocluster [Au20(PP3)4]Cl4 (PP3=tris(2‐(diphenylphosphino)ethyl)phosphine) has been prepared by the reduction of a gold(I)–tetraphosphine precursor in dichloromethane solution. Single‐crystal structural determination reveals that the cluster molecular structure has C3 symmetry. It consists of a Au20 core consolidated by four peripheral tetraphosphines. The Au20 core can be viewed as the combination of an icosahedral Au13 and a helical Y‐shaped Au7 motif. The identity of this Au20 cluster is confirmed by ESI‐MS. The chelation of multidentate phosphines enhances the stability of this Au20 cluster. 相似文献
947.
Mechanistic Insights into the Interface‐Directed Transformation of Thiols into Disulfides and Molecular Hydrogen by Visible‐Light Irradiation of Quantum Dots 下载免费PDF全文
Xu‐Bing Li Zhi‐Jun Li Yu‐Ji Gao Qing‐Yuan Meng Shan Yu Prof. Dr. Richard G. Weiss Prof. Dr. Chen‐Ho Tung Prof. Dr. Li‐Zhu Wu 《Angewandte Chemie (International ed. in English)》2014,53(8):2085-2089
Quantum dots (QDs) offer new and versatile ways to harvest light energy. However, there are few examples involving the utilization of QDs in organic synthesis. Visible‐light irradiation of CdSe QDs was found to result in virtually quantitative coupling of a variety of thiols to give disulfides and H2 without the need for sacrificial reagents or external oxidants. The addition of small amounts of nickel(II) salts dramatically improved the efficiency and conversion through facilitating the formation of hydrogen atoms, thereby leading to faster regeneration of the ground‐state QDs. Mechanistic studies reveal that the coupling reaction occurs on the QD surfaces rather than in solution and offer a blueprint for how these QDs may be used in other photocatalytic applications. Because no sacrificial agent or oxidant is necessary and the catalyst is reusable, this method may be useful for the formation of disulfide bonds in proteins as well as in other systems sensitive to the presence of oxidants. 相似文献
948.
Balancing the Rate of Cluster Growth and Etching for Gram‐Scale Synthesis of Thiolate‐Protected Au25 Nanoclusters with Atomic Precision 下载免费PDF全文
Xun Yuan Bin Zhang Zhentao Luo Qiaofeng Yao Prof. David Tai Leong Prof. Ning Yan Prof. Jianping Xie 《Angewandte Chemie (International ed. in English)》2014,53(18):4623-4627
We report a NaOH‐mediated NaBH4 reduction method for the synthesis of mono‐, bi‐, and tri‐thiolate‐protected Au25 nanoclusters (NCs) with precise control of both the Au core and thiolate ligand surface. The key strategy is to use NaOH to tune the formation kinetics of Au NCs, i.e., reduce the reduction ability of NaBH4 and accelerate the etching ability of free thiolate ligands, leading to a well‐balanced reversible reaction for rapid formation of thermodynamically favorable Au25 NCs. This protocol is facile, rapid (≤3 h), versatile (applicable for various thiolate ligands), and highly scalable (>1 g Au NCs). In addition, bi‐ and tri‐thiolate‐protected Au25 NCs with adjustable ratios of hetero‐thiolate ligands were easily obtained. Such ligand precision in molecular ratios, spatial distribution and uniformity resulted in richly diverse surface landscapes on the Au NCs consisting of multiple functional groups such as carboxyl, amine, and hydroxy. Analysis based on NMR spectroscopy revealed that the hetero‐ligands on the NCs are well distributed with no ligand segregation. The unprecedented synthesis of multi‐thiolate‐protected Au25 NCs may further promote the practical applications of functional metal NCs. 相似文献
949.
Self‐Assembly of Pyridinium‐Functionalized Anthracenes: Molecular‐Skeleton‐Directed Formation of Microsheets and Microtubes 下载免费PDF全文
Dr. Jun Hu Peiyi Wang Prof. Yuan Lin Prof. Jidong Zhang Dr. Mark Smith Dr. Perry J. Pellechia Prof. Song Yang Prof. Baoan Song Prof. Qian Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7603-7607
Two amphiphilic regioisomers, 9‐AP (1‐[11‐(9‐anthracenylmethoxy)‐11‐oxoundecyl]pyridinium bromide), and 2‐AP (1‐[11‐(2‐anthracenyl methoxy)‐11‐oxoundecyl]pyridinium bromide), were synthesized and their assembly behaviors were studied. Due to the anisotropic features of the anthracene structure, different substituted positions on the anthracene ring lead 9‐AP and 2‐AP to adapt “shaver” and “spatula”‐like molecular shapes, respectively, which consequently dictate the structure of their final assemblies. While “shaver”‐shaped 9‐AP assembled into microsheets, driven by π–π interactions, “spatula”‐shaped 2‐AP assembled into microtubular structures, promoted primarily by charge‐transfer interactions. 相似文献
950.
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献